Hiller Davina, Sanglard Dominique, Morschhäuser Joachim
Institut für Molekulare Infektionsbiologie, Universität Würzburg, Röntgenring 11, D-97070 Würzburg, Germany, and Institute of Microbiology, University Hospital Lausanne, Switzerland.
Antimicrob Agents Chemother. 2006 Apr;50(4):1365-71. doi: 10.1128/AAC.50.4.1365-1371.2006.
Overexpression of MDR1, which encodes a membrane transport protein of the major facilitator superfamily, is one mechanism by which the human fungal pathogen Candida albicans can develop increased resistance to the antifungal drug fluconazole and other toxic compounds. In clinical C. albicans isolates, constitutive MDR1 overexpression is accompanied by the upregulation of other genes, but it is not known if these additional alterations are required for Mdr1p function and drug resistance. To investigate whether MDR1 overexpression is sufficient to confer a drug-resistant phenotype in C. albicans, we expressed the MDR1 gene from the strong ADH1 promoter in C. albicans laboratory strains that did not express the endogenous MDR1 gene as well as in a fluconazole-resistant clinical C. albicans isolate in which the endogenous MDR1 alleles had been deleted and in a matched fluconazole-susceptible isolate from the same patient. Forced MDR1 overexpression resulted in increased resistance to the putative Mdr1p substrates cerulenin and brefeldin A, and this resistance did not depend on the additional alterations which occurred during drug resistance development in the clinical isolates. In contrast, artificial expression of the MDR1 gene from the ADH1 promoter did not enhance or only slightly enhanced fluconazole resistance, presumably because Mdr1p expression levels in the transformants were considerably lower than those observed in the fluconazole-resistant clinical isolate. These results demonstrate that MDR1 overexpression in C. albicans is sufficient to confer resistance to some toxic compounds that are substrates of this efflux pump but that the degree of resistance depends on the Mdr1p expression level.
MDR1编码主要易化子超家族的一种膜转运蛋白，其过表达是人类真菌病原体白色念珠菌对抗真菌药物氟康唑及其他有毒化合物产生耐药性增强的一种机制。在临床白色念珠菌分离株中，MDR1的组成型过表达伴随着其他基因的上调，但尚不清楚这些额外的改变对于Mdr1p功能和耐药性是否是必需的。为了研究MDR1过表达是否足以赋予白色念珠菌耐药表型，我们在不表达内源性MDR1基因的白色念珠菌实验室菌株中，以及在已缺失内源性MDR1等位基因的氟康唑耐药临床白色念珠菌分离株及其来自同一患者的匹配的氟康唑敏感分离株中，从强ADH1启动子表达MDR1基因。强制MDR1过表达导致对假定的Mdr1p底物浅蓝菌素和布雷菲德菌素A的耐药性增加，且这种耐药性不依赖于临床分离株耐药性发展过程中发生的其他改变。相比之下，从ADH1启动子人工表达MDR1基因并未增强或仅轻微增强氟康唑耐药性，推测是因为转化体中的Mdr1p表达水平远低于在氟康唑耐药临床分离株中观察到的水平。这些结果表明，白色念珠菌中MDR1过表达足以赋予对该外排泵某些底物有毒化合物的耐药性，但耐药程度取决于Mdr1p表达水平。
